Drive device comprising an eccentric gearing

ABSTRACT

The invention relates to a drive device, for driving a regulating unit. Said device has a gearing ( 20 ) mounted between a motor ( 10 ) and the regulating unit ( 30 ). The gearing ( 20 ) has at least a first gearing stage ( 22 ) which is coupled to an output shaft of the motor ( 10 ) and a subsequent second gearing stage ( 24 ), whereby the second gearing stage ( 24 ) is configured as an eccentric gearing stage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is concerned with a drive device with an eccentricgearing.

2. Description of the Related Art

In many applications of gears, a maximal drive moment is required onlybeginning at a particular point. Such requirements occur for example ingears which are used in a locking function. In the constructionindustry, this could be a window closer or, in the automotive industry,a closure tightening aid, or a gear for closing of air flaps.

If the drive occurs via an electric motor, and if a gearing with aconstant transmission or speed change curve is employed, there resultsthe disadvantage that the ratio of the transmission must be so high onthe one side that the maximal moment can be achieved with the employedmotor. This requires as a rule a high adjustment time or adjustment timeof the gearing. The adjustment time is limited in many applications,such as for example during the closure of an air flap, which must beclosed in response to fire, or in climate control devices or in windowclosers.

In order to maintain the adjustment time within prescribed limits, it isnecessary in this case to employ a stronger and thus more expensivemotor, in order to reduce the transmission ratio and therewith tomaintain the adjustment time within the prescribed limits whileachieving the required drive moment.

It is a further disadvantage, that in the case of stronger motors alsostronger electric currents are needed, whereby also the control of themotor becomes substantially more expensive. In the design of the gearunit thus in many cases a maximum current is not to be exceeded. Even inthe case of a weaker direct current motor there is the problem that thecurrent requirement increases with decreasing motor speed.

A further disadvantage of such a design is that, in the case of thecommonly employed direct current motors, the RPM of the motor dependsupon the required motor moment. The motor has a changing RPM during thisresetting or adjustment. This change in RPM has a negative effect on thesubjective noise sensitivity and is not accepted as such in theabove-described environments of use—in the construction and automobileindustry.

SUMMARY OF THE INVENTION

It is the task of the invention to avoid the above-describeddisadvantages and to produce a drive device in such a manner that therequired drive moment is achieved with a weaker motor and, at the sametime, the adjustment time of the gearing is reduced.

The solution is comprised therein, that instead of a drive withcontinuous transmission, a two-stage drive is employed, wherein thesecond stage is an eccentric gearing. The first stage can be aconventional gearing. Preferably the first gearing stage is a harmonicdrive system or a wave generator as described in detail by applicants inissued European Patent EP 0 918 961 B1 (U.S. Pat. No. 6,220,115 B1). Forthe purpose of disclosure the content of this patent is incorporatedherein by reference. The transmission elements of the therein describedwave generator (also referred to as harmonic-drive-gearing) areplanetary gears.

Eccentric gears are gears with non-constant transmission behavior, andas such are already known. One example of an eccentric gear is describedin DE 197 39 851 A1. Therein the gearing is used for driving awindshield wiper for an automobile. The eccentric gear is hereinexclusively used in order to produce a back and forth movement of thewindshield wiper. The therein described eccentric gearing is however notemployed for achieving a particular transmission power curve or forreducing adjustment times.

One solution according to the invention is also concerned with aprocess, in which the behavior curve of the required drive moment, andthe given motor characteristic curve of the employed driver, aredetermined for the optimal transmission curve, so that therewith theabove-described disadvantages can be avoided. The optimization furtherdistinguishes between the individual types of electric motors, forexample between a direct current motor and a stepping motor.

A particular advantage of the invention is comprised therein, that bythe optimization of the transmission curve during use of a directcurrent motor this can be driven with substantially more constant RPMover the entire range of adjustment, whereby the drive or gear noise issubstantially reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described and explained on the basis of a firstand second illustrative embodiment represented in the figures.

In the figures there is shown:

FIG. 1 shows a flow diagram of the procedure of optimization of aneccentric gear according with the prior art.

FIG. 2 shows a flow diagram of the individual calculation steps of theEuler process.

FIG. 3 shows a flow diagram of the procedure of optimization of aneccentric gear according with the present invention.

FIG. 4 shows an eccentric gear according with the present invention.

FIG. 5 shows a drive process for the design.

DETAILED DESCRIPTION OF THE INVENTION

The invention is further comprised therein, that each individual geartooth has its own individual basic profile, so that each tooth can beoptimized with respect to rigidity, noise, tolerance and degree ofeffectiveness. Particularly in the case of gears not generated byplaning or shaping, that is, for example, gears produced by injectionmolding, sintering or by broaching produced eccentric gears, thereresult significant advantages even in the case of non-involute(non-curved) gears on the basis of the produced undercuts, when thecurvature of the generating cam is too large at points.

The sequence of the adaptation of an eccentric gear occurs iterativelyin multiple steps as follows:

First, from the drive moment curve and the motor characteristic curve afirst optimized transmission curve is determined. From this, the polarcurve or centrode of the eccentric gear is determined. Subsequently froma conventional reference profile, in which however each tooth can bedifferent, the teeth of the eccentric gear are calculated. Subsequently,using a roller simulation the tensions occurring during the movement andthe resulting degrees of effectiveness are determined. Since the degreeof effectiveness curve has an influence on the RPM during the adjustmenttime, with the gears there must now once again be determined the momentcurve and the adjustment time.

If now the behavior is no longer acceptable, a new optimization ofmanufacturing or, as the case may be, optimization calculation, must becarried out, in order to optimally determine and shape or design of thegenerating cam and therewith the gear teeth.

This procedure is represented in detail as a flow diagram in FIG. 1.Reference is expressly made thereto herein.

On the basis of the complex inter-relationships the optimization canonly be calculated and solved using a computer program.

In the following the optimization of an eccentric gear will beillustrated using an example of a direct current motor with a givenmotor characteristic curve according to

M ₁ =M ₁(n) or n ₁ =n(M ₁), i=i(n)

wherein M₁=motor moment, i=motor current, n₁=RPM and a given moment

M ₂ =M ₂(φ₂),

wherein M₂=driven moment, φ=driven rotation angle.

The result of the first optimization is a transmission or speed changecurve or behavior according to

i=i (φ₂),

wherein i=transmission or speed change, φ₂=driven rotation angle.

Further the required adjustment time and maximal current requirement arepreferably reduced as far as possible, and advantageously at the sametime the rotational behavior of the motor and therewith the gear noiseare optimized.

In order to achieve a substantially constant rotation speed of the motorand therewith a reduction in noise, the transmission or speed changebehavior is so selected as a starting value for optimization, that themotor rotational speed remains constant or substantially constant overthe entire or at least substantially the entire adjustment time.

The calculation of the adjustment time of the rotation speed behaviorand the current requirement requires a differential equation system,which in general cannot be explicitly solved. For this reason, asnumeric process there is employed for example an explicit Euler process.

The individual calculation steps of the Euler process are represented inthe flow diagram according to FIG. 2, to which reference is expresslymade.

From the characteristic profile of the two eccentric gears, next thegear geometry is determined. Then the tooth foot tensions, flankpressures and deformation of the teeth in the case of plastic gearwheels are determined and optimized. Further, the effectiveness at eachengagement point is determined. In the next step the calculation of theadjustment times is carried out once again, however this time includingthe degree of effectiveness in each engagement point and therewith thetooth geometries.

The drive process shown as an example in FIG. 5 shows one design for awindow closer as an adjustment device or control device 30 in theconstruction industry with an essentially cosine-shaped curve of thedrive moment (compare FIG. 4). The employed direct current motorindicated with reference number 10 in FIG. 5 has a constant rotationalspeed over almost the entire adjustment range. Its output shaft iscoupled to a first gear stage 22 and the output thereof with a secondgear stage 24. The second gear stage 24 is an eccentric gear. Theoverall gearing is referenced with reference number 20. Therewith theadjustment time can be reduced by 30% and the maximum currentrequirement can be reduced by approximately 40%. In FIG. 4 referencenumbers 22 a and 24 a indicate shafts of the eccentric gear 24 or, asthe case may be, control device 30 and 22 b and 24 b associated gearcurves.

What is claimed is:
 1. A drive device for driving a control device witha gearing (20) connected between a motor (10) and the control device(30), which comprises eccentric gears (22 a, 24 a), wherein the gearing(20) comprises at least a first gear stage (22) coupled to an outputshaft of the motor (10) and constructed as a harmonic drive, and afollowing, second gear stage (24), the second gear stage (24) beingconstructed as an eccentric gear stage.
 2. A drive device according toclaim 1, wherein said motor (10) is a step motor.
 3. A drive deviceaccording to claim 1, wherein said motor (10) is a direct current motor.4. A drive device according to claim 1, wherein the control device (30)is a window closer.
 5. A drive device according to claim 1, wherein thecontrol device (30) is a ventilation flap adjuster.
 6. A drive deviceaccording to claim 5, wherein the control device (30) is in anautomobile.
 7. A drive device according to claim 1, wherein the firstgear stage (22) includes a drive shaft.
 8. A drive device according toclaim 7, wherein said drive shaft is a corrugated drive withtransmission elements selected from the group consisting of camfollowers, slats and planet arms.
 9. A drive device according to claim1, wherein the drive device describes an adjustment path with anadjustment angle of less than 360°.
 10. A drive device according toclaim 9, wherein the second gear stage (24) is dimensioned so that alarger torque in comparison with the start of the regulating operationacts on a control element of the control device (30) in the region ofthe end of the adjustment path.